Depending on a means of sensing, the techniques of estimating traffic flow fall into different categories, namely loop coils, ultrasonic, microwave, active, passive, imaging and magnetic induction, and usually involve detecting vehicles shown in images. Among the aforesaid categories of the techniques of estimating traffic flow, imaging-based detection is becoming more important, because it not only measures the number and speeds of vehicles but also estimates data, such as the length of a queue and the diverting flow rate.
The conventional imaging-based detection technique detects vehicles shown in images by light sensing techniques, but its accuracy is easily affected by any changes in the light rays of visible light, and in consequence vehicles shown in images cannot be detected efficiently. In an attempt to overcome the aforesaid drawbacks of the conventional imaging-based detection technique, a thermal imaging camera-based vehicle detection technique (hereinafter referred to as thermal imaging vehicle detection technique) is put forth. The thermal imaging vehicle detection technique entails performing light sensing and imaging by the infrared light emitted from a vehicle and thus is not affected by any changes in the light rays of visible light; hence, it is effective in detecting vehicles shown in images. Specifically speaking, the thermal imaging vehicle detection technique efficiently detects vehicles shown in images by detecting the infrared light which is reflected off vehicle windows or vehicle bottoms shown in the images.
However, the conventional thermal imaging vehicle detection technique relies merely upon a detection algorithm with a single thermal imaging vehicle feature. Although the detection algorithm with a single thermal imaging vehicle feature is able to detect vehicles shown by thermal imaging, it is predisposed to erroneous judgment in vehicle detection due to variation in background thermal radiation between different seasons or because of heavy traffic, thereby deteriorating the stability and accuracy of thermal imaging vehicle detection. Hence, it is important to overcome the aforesaid drawback of the prior art, that is, erroneous judgment in vehicle detection carried out with the thermal imaging vehicle detection technique.